Secondary recovery



Patented Jan. 15, 1946 7 SECONDARY nncovnar Alva C. Byrns, Oakland, Calif., asslgnor to Union Oil Company of California, Los Angcles, Califl, a corporation of California No Drawing.

Application October 4, 1943,

Serial No. 504,901

11 Claims.

This invention relates to a method of recovering oil from subterranean oil-bearing formation, and more particularly to the recovery of heavy viscous oils from wells.

It is well known that .oil contained in oilbearing formations as a general rule is contained in solid rock strata'or densely compacted sand. This oil will not flow freely within said sands unless subjected to an expelling force such as gas or other pressure medium. In some cases the oil is subjected to a hydrostatic pressure, but in all cases the main pressure is exerted by condensed vapors and absorbed gases. During the initial period of operation of said production well, the above mentioned pressure within the formation may be around about several hundred pounds, this locked-in pressure in the dense sands or solid rock indicates a condensation to the liquid state of all the lighter hydrocarbon vapors and a very high percentage of absorption of the hydrocarbon gases in the oil. The pressure under these circumstances is not so much on the oil as, in reality, within the oil.

When the production well is drilled through the rock capping and into the oil-sands, the oil begins to liberate the gases with which it is charged and the liquefied volatile hydrocarbons begin to volatilize with great force and the oil is driven forward toward said production well by the movement of the gas, the expelling action beginning near the production well and gradually extending iurther away into the formation. As the light vapors and oil escape, the oil remalning within the densely compacted sands becomes thicker and more viscous and is forced through the line interstices of the rock with ever increasing dimculties. Eventually the oil becomes so viscous, the gas pressure so weak and the capillary resistance so great that the well ceases almost entirely to yield oil, as the force of gravity alone is not suficient to cause said oil to flow in itsthickened condition towards said production well. It is due to this altered condition of the oil in the sandwhich results in the abandonment of a well when only about 60 to 70% til two above described fields a problem similar in nature arises, i. e., the recovery of the said heavy viscous oils.

It has been the practice in recovering heavy viscous oils from producing wells which penetrate oil-bearing formations containing said viscous oils and fields that are approaching depletion, to force flood water through the oilbearing sands from an input well or wells centrally located with respect to several producing wells, for the purpose of driving the oil into the latter. The above mentioned method has proved itself of somewhat limited value in many instances, because of the high viscosity of said oil and the high capillary resistance within the interstices. Another disadvantage in the above method, is the large volumes of water and high pressures required to drive the water and viscous oils from the interstices.

Another method of secondary recovery which has been resorted to is to recycle a petroleum fraction through an input well and into the vis cous oil formation so as to dissolve said heavy viscous oils and thereby reduce the efiective viscosity so that the oil will flow more readily in the direction of the production well or wells, This process has not been entirely satisfactory, because the various distillates used were not sufficiently high in solvent power to retain. the asphalt in solution and resulted in carrying along a part of the lighter fractions with a rcsuiting asphalt precipitate which plugged the oil-bearing formation and well casing.

I have discovered a process whereby the heavy viscous oils and other hydrocarbons existing within the subterranean strata and sands can be more fully and economically recovered by above described methods, and whereby rate of flow of the viscous oils and other hydrocarbons can be greatly augmented, and furthew more, whereby that portion of the oil which is ordinarily non-recoverable, is by the use of my invention rendered available and is thereby recovered.

in carrying out the process of my invention the following procedure is employed. A nonviscous highsulfur petroleum fraction with a viscosity below about 1,000 seconds determined by the Saybolt Universal viscosimeter at 100 F. and a sulfur content in excess of 5% by weight is injected into the formation under pressure through an injection well. The sulfur in the above mentioned high sulfur fraction is contained in the form of organic sulfur compounds. The use of the term injection well is not limited to an input well separate and distinct from a production well but includes a production well which is used for the dual purpose of introducing said high sulfur fraction into the formation and removal of oil therefrom. This injection is intended to be used continuously or at frequent intervals, preferably not as a separate operation from the oil-pumping at the production well, but coincident therewith, and in integral combination. The above mentioned non-viscous high sulfur fraction, which is characterized by its high solvent power for keeping asphalt or heavy oils in solution at varying temperatures, entering the oil formation will contact and dissolve said heavy oil and thereby reduce the etfectlve viscosity of said heavy oil. The solvent power of this non-viscous sulfur fraction with theheavy oils dissolved therein will allow the same to fiow more readily towards the production well without the detrimental effect of precipitating said asphalt.

As a specific example of the applicationbf this invention, I used a non-viscous high sulfur petroleum fraction with a sulfur content of Prior to the a the conventional pumping units in a field not previously subjected to secondary, recovery, such as water flooding or gas repressuring. This field was of the second above described type., i. e., the

oil was of' a heavy viscous nature during the entire life of said field. According to the'invention, the input well was treated with the above mentioned high sulfur content material and iniected therein under suflicient pressure to cause same to enter the oil-bearing formation. This treatment was continued for a period of twenty days, during which time the pumps on the above" mentioned production wells continued to operate. Durin the twenty day period the production of oil increased from the above mentioned 30 barrels per day up to about 110 barrels per day at the four production wells. The above mentioned 110 barrels were computed by sub.- tr'acting the above mentioned introduced high sulfur content fraction. It is evident that during the treatment above described, the high sul-' fur solvent dissolved the'heavy oil and asphalt therein and carried same to production wells.

In the above described practlcemf my invention, I operated by means of an input well, al-" though this method is preferable I do not wish tached to carbon atoms are substituted by mercapto (RS- groups, wherein the R may be an aromatic or aliphatic (including cycloaliphatic) hydrocarbon group such as a benzyl, tolyl, methyl, isopropyl, butenyl, cyclohexyl, or like group, or a heterocyclic group such as a radical derived from dioxane, morpholine and the like.

Those of the mercapto substituted carboxylic acids which may be considered as homologs of ethyl mercaptoacetic acid may be represented by the following generalized formula:

RB x1 cr-ooon Where X1 and X: are alkyl groups, unsaturated radicals derived from alkyl groups by loss of hydrogen, aralkyl groups, carboxylic groups, het- -erocyclic rings of RS groups the same or different from the RS groups shown and where R represents an alkyl, aralkyl, carbocyclic or heterocyclic group, or an unsaturated radical derived from an alkyl group byloss of hydrogen and Y represents (Cl-I2) where n=0 or an integer which may be as high as 5 or higher. Ethyl mer-' capto-acetic acid is representedby the above formula, where R is an ethyl (CaHs) group, X1 and X: are both hydrogen, and 11:0.

Ethyl mercaptoacetic acid maybe prepared by treating chloroacetic acid with ethyl mercaptan and the other mercapto-substituted carboxyllow boiling petroleum fractions; whether crude I distillates or products of pyrolysis or other treatment thereof. The'operating conditions employedin the solvent extraction, such as temperatures and volumes of selective solvent etc., may be adjusted according to well-known principles to obtain the desired degree of extraction. The extract may be separated from the selective solvent by conventional methods such as distillation, extraction with a third solvent, etc.

Other selective solvents which may be employed in the solvent extraction are alkaline agents such as solutions of caustic soda, caustic potash, and the like, which may contain solvent modifiers, suchas methanol, isobutyric acid salts,

and the like. These alkaline agents are particu to be limited by same because beneficial results I may also be obtained by introducing the high sulfur fraction through the production well or tlve solvents which may be broadly described as mercapto-substituted carboxylic acids. These may be condensed as organic carboxylic acids such as formic, acetic, succinic. benzoic and like acids whether aliphatic or aromatic in character, wherein one or more hydrogen atoms atby distillation, cracking or coking of these crudes,

Besides the above selective solvents, which are especially selective for sulfur compounds, well known selective solvents such as sulfur dioxlde, phenol. furfural, or any other suitable selective solvents may be employed.

Other petroleum fractions, such as n n-viscous' lytic de-" high sulfur fractions obtained by p composition catalytic or non-catalytic, of high sulfur crude oils such as those found in the Santa Marla Valley, Oxnard and Gate Ridge fields,

located in the State of: California have proved very beneficial. Although the fractions obtained containing in excess of 5% sulfur, by weight,

are eflective in keeping the asphalt in, solution, still more satisfactory results are obtained if the recycle fractions are those :containing 10% sulfur or more. As mentioned above, the preferred type of material may consist of fractions asaaevr all of these sulfur compounds have sufllciently high solvent power to keep the asphalt in solution. The only limitation on boiling point range being that of viscosity.

The foregoing description of my invention is not to be taken as limiting my invention but only as illustrative thereof since many variations may be made by those skilled in the art without departing from the scope of the following claims:

I claim:

l. The method of increasing the production of an oil weli wherein a solvent is injected into oil-bearing formations which contain heavy viscous ,oils surrounding an input well and oil is removed from a production well, the process which comprises injecting a solvent consisting of a non-viscous petroleum fraction having a suli'ur content in excess of 5% by weight into the said input well. causing said solvent to dissolve heavy oils within said oil-bearing formation, and removing said solvent and heavy oil from said production well.

2. A process according to claim 1 in which the solvent is a non-viscous product of pyrolytic decomposition of a high sulfur petroleum fraction.

3. The method of increasing the production of an oil well wherein a solvent is injected into oilbearing formations which contain heavy viscous oils surrounding an input well and oil is removed from a production well, the process, which comprises injecting a solvent consisting of a nonviscous extract having a sulfur content in excess of 5% by weight produced by solvent extraction of a sulfur containing petroleum fraction into the said input well, causing s'aid solvent to dissolve heavy oils within said oil-bearing formation, and removing said solvent and heavy oil from the production well.

4. A process according to claim 3 in which the petroleum fraction is a product of pyrolytic decomposition.

5. A process according to claim 3 in which the extract is one produced by solvent extraction with mercapto-substituted carboxylic acid.

6. A process according to claim 3 in which the solvent has a sulfur content greater than 10%.

'I. A process according to claim 3 in which the extract is one produced by solvent extraction with an alkaline selective solvent and which consists predominantly of mercaptans.

8. A process according to claim 3 in which the extract is one produced by solvent extraction with a solvent solution comprising a mercaptosubstituted carboxylic acid.

9; A process according to claim 3 in which the extract is one produced by solvent extraction with ethyl thioglycollic acid.

10. A process according to claim 3 in which so the extract is one produced by solvent extraction with caustic soda, and which consists predominantly of mercaptans. .0

11. A process according to claim 1 in which the petroleum fraction has a sulfur content in ex- 85 cess of 10% by weight.

ALVA C. BYRNS. 

